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Abstract:

A control system for a touch screen is provided. The control system
includes a voltage-level shifter between a screen controller and a touch
controller. The voltage-level shifter level-shifts a common voltage for
driving the screen to a corresponding timing signal with an input signal
range acceptable by the touch controller.

Claims:

1. A control system for a touch screen, the touch screen comprising a
screen and a touch sensor, the control system comprising: a screen
controller, for generating a common voltage to the screen, the common
voltage varying within a first signal range; a voltage-level shifter,
having an input terminal and an output terminal, the input terminal being
coupled to the common voltage; the voltage-level shifter providing a
timing signal at the output terminal according to the common voltage, the
timing signal varying within a second signal range, the first signal
range being different from the second signal range; and a touch
controller, coupled to the output terminal, for controlling the touch
sensor according to the timing signal.

2. The control system according to claim 1, wherein the voltage-level
shifter comprises: an alternating-current (AC) coupling circuit, coupled
between the input terminal and the output terminal, for filtering out a
direct-current (DC) component in the common voltage; and a level
adjuster, coupled to the output terminal, for adjusting the timing signal
to the second signal range.

3. The control system according to claim 2, wherein the AC coupling
circuit comprises a capacitor coupled between the input terminal and the
output terminal.

4. The control system according to claim 2, wherein the level adjuster
comprises: a first resistor, coupled between a first operating voltage
and the output terminal; and a second resistor, coupled between the
output terminal and a second operating voltage.

5. The control system according to claim 2, wherein the level adjuster
and the touch controller are packaged in a same chip.

6. The control system according to claim 2, wherein the level adjuster
comprises: a resistor, coupled between a predetermined operating voltage
and the output terminal; and a diode, having an anode and a cathode
respectively coupled to the predetermined operating voltage and the
output terminal.

7. The control system according to claim 2, wherein the diode is a
Schottky diode.

8. The control system according to claim 1, wherein the touch controller
comprises: a converter, coupled the output terminal, for generating an
indication signal according to the timing signal; and a sensing timing
circuit, coupled to the converter, for providing a gate control signal
according to the indication signal, the gate control signal comprising a
plurality of non-sensing periods and a plurality of sensing periods, the
non-sensing periods covers a plurality of transitions of the indication
signal, and the indication signal being maintained in a steady state in
the sensing periods.

9. The control system according to claim 8, wherein the converter is a
comparator.

10. The control system according to claim 8, wherein the converter is a
Schmitt trigger.

11. The control system according to claim 1, wherein the touch screen
contains no shielding layer.

12. The control system according to claim 1, wherein the screen
controller is fabricated as a first integrated circuit and the touch
controller is fabricated as a second integrated circuit.

Description:

[0001] This application claims the benefit of Taiwan application Serial
No. 101109372, filed Mar. 19, 2012, the disclosure of which is
incorporated by reference herein in its entirety.

BACKGROUND

[0002] 1. Technical Field

[0003] The disclosure relates in general to a control system for a touch
screen, and more particularly to a control system that, by utilizing a
voltage-level shifter, converts a common voltage for driving a screen to
a timing signal acceptable by a touch controller and accordingly controls
a touch sensing timing.

[0004] 2. Description of the Related Art

[0005] A touch screen combining touch sensing of a touch sensor and a
display function of a screen provides a user-friendly and intuitive
control interface, and is one of the most prevalent human-machine
interfaces in the modern world.

[0006]FIG. 1 shows a sectional view of a conventional touch screen 10.
The touch screen 10 engages a touch sensor 12 and a screen 14 via an
adhesive layer ADVp. The touch sensor 12 includes a cover lens layer CLp,
an adhesive layer OCAp, an electrode layer ITO_SRp, an isolating layer
PET1p, an electrode layer ITO_SLD and an isolating layer PET2p. For
example, the cover lens layer CLp is made of glass or acrylic, the
adhesive layer OCAp is an optically clear adhesive layer, the electrode
layers ITO_SRp and ITO_SLD are conductive layers formed from indium tin
oxide (ITO), and the isolating layers PET1p and PET2p are non-conductive
isolating layers formed by polyester films. The electrode layer ITO_SRp
includes a plurality of sensing electrodes. When touch control occurs on
the cover lens layer CLp, the sensing electrodes distributed at different
positions are respectively coupled to capacitance changes in different
values. Thus, a touch position can be determined according to the
positions of the sensing electrodes and the capacitance changes coupled
to the sensing electrodes.

[0007] For example, the screen 14 is a crystal-liquid display (LCD) panel
including an upper glass substrate TG, an electrode layer ITO_VCOMp and a
liquid crystal structure LCSp. The electrode layer ITO_VCOMp is a
conductive layer formed by ITO. The liquid crystal structure LCSp
includes pixel electrodes in a matrix arrangement in another ITO
electrode layer (not shown). Each of the pixel electrodes forms a pixel
with a thin-film transistor (not shown), while liquid crystal is filled
between the pixel electrodes and the electrode layer ITO_VCOMp. The
electrode layer ITO_VCOMp extends along a planar direction of the screen
14 to cover the pixel electrodes of the screen to conduct a common
voltage. Under the control of a gate voltage, the thin-film transistors
conduct a source voltage to the corresponding pixel electrodes.
Therefore, in the pixels, the source voltage conducted with the pixel
electrodes drives the crystal liquid filled between the pixel electrodes
and the electrode layer ITO_VCOMp together with the common voltage
present on the electrode layer ITO_VCOMp to change a status of the liquid
crystal. For example, an arrangement direction and thus a transparency of
the liquid crystal is changed, allowing the pixels to present an image
having different and distinct brightness and color.

[0008] As the liquid crystal is driven by a constant-polarity voltage in
the long term, particle characteristics of the liquid crystals can be
damaged to result in a residual image on the screen. To prevent the
residual image, the common voltage transmitted on the electrode layer
ITO_VCOMp periodically switches to different levels to perform polarity
inversion. Since the touch sensor 12 is very much alike the electrode
layer ITO_VCOMp in the screen 14 and the electrode layer ITO_VCOMp has a
substantial area, the conventional touch sensor 12 is required to be
provided with a shielding electrode layer ITO_SLD, so as to prevent
transition of the common voltage to be coupled to the sensing electrodes
of the electrode layer ITO_SRp. In the absence of the electrode ITO_SLD,
the transient state triggered by the transition of the common voltage
shall be coupled to the sensing electrodes of the electrode layer ITO_SRp
to undesirably affect touch sensing.

SUMMARY

[0009] The present invention discloses a control system for a touch screen
including a screen and a touch sensor. The control system includes a
screen controller, a voltage-level shifter and a touch controller. The
screen controller generates a common voltage which drives the screen and
varies within a first signal range. The voltage-level shifter has an
input terminal and an output terminal. The output terminal of the
voltage-level shifter is coupled to the common voltage to allow the
voltage-level shifter to provide a timing signal at the output terminal
according to the common voltage. The timing signal varies within a second
signal range different from the first signal range. The touch controller
is coupled to the output terminal and controls the touch sensor according
to the timing signal.

[0010] Preferably, the voltage-level shifter includes an
alternating-current (AC) coupling circuit and a level adjuster. The AC
coupling circuit, coupled between the input terminal and the output
terminal of the voltage-level shifter, filters out a direct-current (DC)
component in the common voltage, and reflects a filtered result at the
output terminal. The level adjuster, coupled to the output terminal,
controls the second signal range of the timing signal.

[0011] Preferably, the AC coupling circuit includes a capacitor coupled
between the input terminal and the output terminal of the voltage-level
shifter.

[0012] Preferably, the level adjuster includes a first resistor and a
second resistor. The first resistor has two terminals respectively
coupled to a first operating voltage (e.g., a positive voltage) and the
output terminal of the voltage-level shifter. The second resistor has two
terminals respectively coupled to the output terminal of the
voltage-level shifter and a second operating voltage (e.g., a ground
voltage). The AC coupling circuit filters out the DC component in the
common voltage, and reflects the filtered result at the output terminal.
The first resistor and the second resistor divide the voltage between the
first operating voltage and the second operating voltage. A DC voltage
established from the voltage dividing is loaded on the filtered resulted
at the output terminal to provide another DC component to the
DC-component-removed common voltage to become the timing signal.

[0013] Preferably, the level adjuster includes a resistor and a diode. The
resistor is coupled between the second operating voltage and the output
terminal. The second diode has an anode and a cathode respectively
coupled to the second operating voltage and the output terminal. When the
DC-component-removed common voltage is reflected at the output terminal,
an upper limited of the second signal range of the timing signal is
established by the second operating voltage plus a resistor cross
voltage, and a lower limit of the second signal range of the timing
signal is established by the second operating voltage minus a forward
bias between the anode and the cathode of the diode.

[0014] Preferably, the level adjuster in the voltage-level shifter and the
touch controlled are packaged in a same chip, the screen controller is
packaged in another chip, and the AC coupling circuit in the
voltage-level shifter is coupled between the two chips. Alternatively,
the touch controller and the screen controller are two different chips,
and the voltage-level shifter is coupled between the two chips.

[0015] Preferably, the touch controller includes a converter and a sensing
timing circuit. The converter, coupled to the output terminal of the
voltage-level shifter, provides a digital indication signal according to
the timing signal. The sensing timing circuit, coupled to the converter,
provides a gate control signal according to the indication signal. The
gate control signal includes a plurality of non-sensing periods and a
plurality of sensing periods. The non-sensing periods cover the
transitions of the indication signal, while the indication signal is
maintained at a steady state in the sensing periods. Thus, the touch
controller controls the touch sensor according to the gate control signal
to prevent interferences of the transition of the common voltage. For
example, the touch controller stops sensing in the non-sensing periods,
and/or discards sensing results of the non-sensing periods.

[0017]FIG. 2 is a schematic diagram of a control system and a touch
screen according to one embodiment of the present invention.

[0018]FIG. 3 is an operating timing diagram of the control system in FIG.
2

[0019]FIG. 4 is a schematic diagram of a control system according to an
alternative embodiment of the present invention.

[0020]FIG. 5 is a schematic diagram of a touch screen according to one
embodiment of the present invention.

[0021] In the following detailed description, for purposes of explanation,
numerous specific details are set forth in order to provide a thorough
understanding of the disclosed embodiments. It will be apparent, however,
that one or more embodiments may be practiced without these specific
details. In other instances, well-known structures and devices are
schematically shown in order to simplify the drawing.

DETAILED DESCRIPTION

[0022]FIG. 2 shows a schematic diagram of a control system 30a
accompanying with a touch screen 20 according to one embodiment of the
present invention. The touch screen 20 includes a screen 24 and a touch
sensor 22. The control system 30a includes a screen controller 26, a
voltage-level shifter 32a and a touch controller 28. The screen
controller 26 provides a common voltage VCOM for driving the screen 24.
Nodes Ni and Nc of the voltage-level shifter 32a are respectively
regarded as an input terminal and an output terminal of the voltage-level
shifter 32a. The input terminal is coupled to the common voltage VCOM at
the node Ni to allow the voltage-level shifter 32a to provide a
corresponding timing signal Sa at the output terminal at the node Nc
according to the common voltage VCOM. The touch controller 28 is coupled
to the node Nc, and controls the touch sensor 22 according to the timing
signal Sa.

[0023] In this embodiment, the voltage-level shifter 32a includes an
alternating-current (AC) coupling circuit 34 and a level adjuster 36a.
The AC coupling circuit 34 includes a capacitor C1 coupled between the
nodes Ni and Nc. The capacitor C1 of the AC coupling circuit 34 filters
and removes a direct-current (DC) component in the common voltage VCOM,
and reflects a filtered result at the node Nc. The level adjuster 36a is
coupled to the node Nc, and controls a signal range of the timing signal
Sa. The level adjuster 36a includes two resistors R1 and R2. The resistor
R1 has two terminals respectively coupled to an operating voltage VDD,
e.g., a positive voltage, and the node Nc. The resistor R2 has two
terminals respectively coupled to the node Nc and another operating
voltage VSS, e.g., a ground voltage. For example, the operating voltages
VDD and VSS are DC operating voltages of the touch sensor 28.

[0024]FIG. 3 shows operating timing waveforms of the voltage-level
shifter 32a and the touch controller 28. A horizontal axis in the
waveforms represents time. To invert a driving polarity, the common
voltage VCOM switches between a level V1t and a level V1b, so that a
peak-to-peak signal range of the common voltage VCOM is between the
levels V1t and V1b. Since the common voltage VCOM is for driving the
screen 24, the signal range is determined by characteristics of the
screen 24. For example, the level V1t as an upper limit of the signal
range is 4V, and the level V1b as a lower limit is -1V. When the common
voltage VCOM switches from the level V1b to the level V1t, a rising-edge
transient occurs. When the common voltage VCOM switches from the level
V1t to the level V1b, a falling-edge transient occurs. Both the
rising-edge and falling-edge transients interfere in the touch sensing of
the touch sensor 22. Preferably, the touch sensing mechanism avoids the
transition of the common voltage VCOM according to a change in the common
voltage VCOM. However, the signal range of the common voltage VCOM is
tailored for requirements of the screen 24, and does not satisfy a rated
input signal range acceptable by the touch controller 28. In this
embodiment, the voltage-level shifter 32a converts the common voltage
VCOM to the timing signal Sa acceptable by the touch controller 28.

[0025] In the voltage-level shifter 32a, the AC coupling circuit 34
filters out the DC component in the common voltage VCOM and reflects the
filtered result at the node Nc, and the resistors R1 and R2 perform
voltage dividing between the operating voltages VDD and VSS. As shown in
FIG. 3, the upper and lower limits of the signal range of the timing
signal Sa are respectively adjusted to levels V2t and V2b by the
voltage-level shifter 32a. The levels V2t and V2b fall within the rated
input signal range of the touch controller 28, so that the timing signal
Sa can be accepted by the touch controller 28. Further, the transition of
the timing signal Sa still follows the transition of the common voltage
VCOM, so that the touch controller 28 is allowed to control the touch
sensing according to the timing signal Sa.

[0026] In this embodiment, values of the resistors R1 and R2 are designed
according to the rated input signal range defined by specifications of
the touch controller 28, such that the levels V2t and V2b fall within the
rated input signal range, e.g., between 0V to 5V. For example, assuming a
period in which the common voltage VCOM is maintained at the level V1t is
a period T1 and a period in which the common voltage VCOM is maintained
at the level V1b is a period T2, the level V2t=V1t-Vdc+Vdiv and
V2b=V1b-Vdc+Vdiv; where Vdc=(T1*V1t+T2*V1b)/(T1+T2) represents the DC
component in the common voltage VCOM, and Vdiv=(VDD*R2+VSS*R1)/(R1+R2)
represents the DC voltage established by the voltage dividing of the
level adjuster 36a.

[0027] The touch controller 28 includes a converter 38 and a sensing
timing circuit 40. The converter 38 is coupled to the node Nc of the
voltage-level shifter 32a, and provides a digital indication signal Sd
according to the timing signal Sa. For example, the converter 38 is a
comparator. When the timing signal Sa is greater than a predetermined
value, the indication signal reflects a logic 1, and when the timing
signal is smaller than the predetermined value, the indication signal
reflects a logic 0. Alternatively, the converter 38 is a Schmitt trigger.
The sensing timing circuit 40, coupled to the converter 38, receives the
indication signal Sd and provides a gate control signal Sg according to
the indication signal Sd. The gate control signal Sg includes a plurality
of non-sensing periods Tns and a plurality of sensing periods Ts. The
non-sensing periods Tns cover the transitions in the indication signal
Sd, as well as the timing signal Sa and the common voltage VCOM. In the
sensing periods Ts, the indication signal Sd/the timing signal Sa/the
common voltage VCOM are maintained at a steady state. The non-sensing
periods Tns cover sensing-interference-prone periods before and after the
transition, and the non-sensing periods avoid the sensing periods. Thus,
the touch controller 28 controls the touch sensor 22 according to the
gate control signal Sg to prevent interferences of the transition of the
common voltage VCOM. For example, the touch controller 28 stops sensing
in the non-sensing periods Tns, and/or discards sensing results of the
non-sensing periods Tns.

[0028]FIG. 4 shows a control system 30b according to another embodiment
of the present invention. The control system 30b is applied to the touch
screen 20. The screen controller 26 controls the screen 24 in the touch
screen 20, and the touch controller 28 controls the touch sensor 22 in
the touch screen 20. For example, the screen controller 26 provides the
screen 24 with the common voltage VCOM and/or associated timing signals
for controlling a gate voltage and a source voltage required by the
screen 24. The touch controller 28 charges and discharges sensing
electrodes (not shown) in the touch sensor 22 to detect capacitance
changes coupled to the sensing electrodes according to charge variances.

[0029] The control system 30b includes a voltage-level shifter 32b for
converting the common voltage VCOM at the node Ni (the input terminal) to
the timing signal Sa at the node Nc (the output terminal). Thus, the
transition of the timing signal Sa follows the transition of the common
voltage VCOM, and allows the signal range of the timing signal Sa to
satisfy the rated input signal range acceptable by the touch controller
28. The voltage-level shifter 32b includes an AC coupling circuit 34 and
a level adjuster 36b. For example, the AC coupling circuit 34 is
implemented by a capacitor C2. The level adjuster 36b includes a resistor
R3 and a diode D, the resistor R2 is coupled between the operating
voltage VSS and the node Nc, and the anode and the cathode of the diode D
are respectively coupled to the operating voltage VSS and the node Nc.

[0030] Operation details of the voltage-level shifter 34b shall be
described with reference to the timing waveforms in FIG. 3. The AC
coupling circuit 34 filters out the DC component in the common voltage
VCOM. When the DC-component-removed common voltage VCOM is reflected at
the node Nc, in a period T1, the diode D is not conducted, and the level
V2t as the upper limit of the signal range of the timing signal Sa is
established by the operating voltage VSS plus the cross voltage of the
resistor R3; in a period T2, the diode D is forward-biased and is
conducted to the node Nc via the operating voltage VSS, and so the level
V2b as the lower limit of the signal range of the timing signal Sa is the
operating voltage VSS minus the forward bias between the anode and the
cathode of the diode D. Therefore, the level V2b is lower than the
operating voltage VSS. Preferably, for example, the diode is implemented
by a Schottky diode. Since the forward bias of a Schottky diode is rather
small (e.g., 0.2V), the lower limit of the level V2b is allowed to
approximate the second operating voltage VSS and to be covered within the
rated input signal range of the touch controller 28.

[0031] As shown in FIGS. 2 and 4, the touch controller 28 is capable of
avoiding the transition in the common voltage VCOM through the timing
signal Sa obtained by voltage-level shifting the common voltage VCOM, so
that the touch sensing stays unaffected from the transition of the common
voltage VCOM. Preferably, an electrode layer for shielding is eliminated
in the touch sensor of the touch screen. FIG. 5 shows the touch screen 20
according to one embodiment of the present invention. The touch screen 20
includes the touch sensor 22 engaged with the screen 24 via an adhesive
layer ADV. For example, the touch sensor 22 is a capacitive touch sensor,
and includes a cover lens layer LC, e.g., made of glass or acrylic, an
adhesive layer OCA, e.g., an optically clear adhesive layer, an electrode
layer ITO_SR, e.g., a conductive layer formed from ITO, and isolating
layer PET1, e.g., a polyester film. Accordingly, the electrode layer for
shielding can be eliminated. The electrode layer ITO_SR includes a
plurality of sensing electrodes. When touch control is performed on the
cover lens layer CL, the sensing electrodes distributed at different
positions possesses coupling capacitance changes in different values. The
touch controller 28 (e.g., in FIGS. 2 and 4) is coupled to the sensing
electrodes, so as to detect the capacitance changes coupled to the
sensing electrodes to determine the touch position.

[0032] For example, the screen 24 is an LCD panel including an upper glass
substrate TG, an electrode layer ITO_VCOM and a liquid crystal structure
LCS. The electrode layer ITO_VCOM is a conductive layer formed from ITO.
The liquid crystal structure LCS includes pixel electrodes in a matrix
arrangement in another ITO electrode layer (not shown). Each of the pixel
electrodes jointly forms a pixel with a thin-film transistor (not shown).
Further, liquid crystals are filled between the pixel electrodes and the
electrode layer ITO_VCOM. The electrode layer ITO_VCOM extends along a
planar direction of the screen 24 to cover the pixel electrodes of the
screen 24 to conduct the common voltage VCOM. Under the control of the
gate voltage, the thin-film transistors conduct the source voltage to the
corresponding pixel electrodes. Therefore, in the pixels, the source
voltage conducted with the pixel electrodes drives the crystal liquid
filled between the pixel electrodes and the electrode layer ITO_VCOM
together with the common voltage transmitted on the electrode layer
ITO_VCOM to change a status of the liquid crystal. For example, an
arrangement direction and thus a transparency of the liquid crystal is
changed, allowing the pixels to present an image having different and
distinct brightness and color.

[0033] In an alternative embodiment, the screen controller 26 and the
touch controller 28 are realized as two different control chips. The
voltage-level shifter 32a (32b) is disposed on the circuit board to be
coupled between the screen controller 26 and the touch controller 28. In
yet another embodiment, the screen controller 26 is packaged in a first
chip, the voltage-level shifter 36a (36b) of the voltage-level shifter
32a (32b) and the touch controller 28 are packaged in a second chip, and
the AC coupling circuit 34 is disposed on the printed circuit board. That
is to say, the AC coupling circuit 34 is coupled to the voltage-level
shifter 36a (36b) in the second chip via a pin of the second chip to
realize the voltage-level shifter 32a (32b).

[0034] As illustrated with the foregoing embodiments, the present
invention discloses disposing a voltage-level shifting circuit between
the screen controller and the touch controller, so that the touch
controller is allowed to eliminate interferences of the common voltage
upon touch sensing by utilizing the common voltage signal of the screen
controller without increasing pin-out. Thus, accuracy of the touch
sensing is ensured, the structure of the touch screen is simplified for
reducing costs of the touch screen, and the characteristics and
performance as well as a yield of the touch screen are optimized.

[0035] It will be apparent to those skilled in the art that various
modifications and variations can be made to the disclosed embodiments. It
is intended that the specification and examples be considered as
exemplary only, with a true scope of the disclosure being indicated by
the following claims and their equivalents.